Conventionally, in the automobile and the like, there is a fuel-filling aperture opening-closing device which blocks the fuel-filling aperture formed in one end of a filler pipe by a screw type filler cap. In such fuel-filling aperture, at each fuel filling, the filler cap has to be removed and put on so as to require additional work. Also, sometimes there occurs a mistake of forgetting to put on the removed filler cap. In order to solve the aforementioned problem of the fuel-filling aperture, there is a fuel-filling aperture opening-closing device which openably and closably blocks the fuel-filling aperture by a flap valve, which can be opened by inserting a fuel-filling nozzle (for example, Patent Document 1).